FACT, THEORY AND MYTH ON THE SPREAD OF AIDS

By LAWRENCE K. ALTMAN

Published: February 15, 1987

As AIDS continues its spread, mounting fear over the epidemic has been matched by persistent confusion over how the virus that causes the disease is transmitted.

More than 30,000 cases of acquired immune deficiency syndrome have been reported in the United States since 1981, when the disease was first identified. More than half the patients have died. Most victims in this country have been homosexual men and intravenous drug abusers.

Four percent of the cases have been attributed to the spread of the virus through heterosexual intercourse with a member of the known high-risk groups: bisexual men, drug abusers or those infected by contaminated transfusions or blood products. An unknown share of an additional 3 percent of cases with undetermined causes may have spread through heterosexual intercourse as well.

Part of the mystery and fear about AIDS arises from the fact that many carriers of the virus are not aware of it. The virus can lurk in the body without causing disease and, among those who develop AIDS, the average time between infection and diagnosis of AIDS may be five years or more.

While much remains to be learned about AIDS, scientists assert with confidence that studies of victims and disease patterns have provided a clear picture of how the virus has spread in this country, and how it has not. Q. How does AIDS spread? Many studies have documented the spread of the AIDS virus to an uninfected person through anal or vaginal intercourse with an infected person; through exchanges of blood, such as on contaminated hypodermic needles; from infected mothers to their infants before or during birth, and possibly through breast-feeding of infants.

Many studies have shown that people do not become infected with the AIDS virus as a result of routine, nonintimate contacts in the home or workplace. Q. Who is now infected with the AIDS virus?

Experts estimate that up to 1.5 million Americans are infected with the AIDS virus. Most are homosexual men and intravenous drug users, but a small, perhaps growing portion are men or women who were infected through heterosexual intercourse with a drug user or a bisexual man. Each infected person is presumed to be capable of spreading the virus to others through sexual intercourse or through blood, as in sharing contaminated needles.

Anyone who has had sexual relations with a homosexual or bisexual man in the last decade, or who has used an unsterile needle to take drugs, is at risk of infection. The infection was rare in the United States in the late 1970's, then spread among homosexual men and drug users exponentially in the early 1980's.

Q. How can a person tell if he or she is infected with the AIDS virus?

The blood test for AIDS infection detects the presence of AIDS virus antibodies, substances the body produces in reponse to invasion by the virus. Those who fear they may be infected can get the blood test through a personal doctor or through anonymous testing centers in many cities.

Q. What proportion of those infected with the virus will develop AIDS?

Scientists believe that the infection persists for life. Only with time will scientists learn what proportion of virus carriers develop AIDS or related afflictions. According to recent estimates by the Federal Centers for Disease Control in Atlanta, from 20 percent to 30 percent of carriers will develop AIDS within five years of initial infection.

Q. Are some types of sexual intercourse more dangerous than others?

Many experts believe that the virus spreads more readily in anal intercourse than in vaginal intercourse because anal sex often involves breaks in rectal tissues, thus allowing easier entry of the virus into the bloodstream. Studies suggest that the receptive partner in anal sex is at greater risk. One study has suggested that the virus may be able to directly infect cells in the colon.

Q. Can the virus spread from an infected person in vaginal intercourse?

Several studies have clearly shown that it can, and that it can spread from a man to a woman or from a woman to a man. Some experts believe transmission occurs far less often from a woman to a man than from a man to a woman, but this point is debated. The virus has been found both in semen and in vaginal secretions of infected people.

Q. How is the virus transmitted in vaginal intercourse?

Scientists are not certain. One theory is that the virus passes through invisible breaks in the surface inside the vagina or on the penis. Some experts believe the virus may also enter through mucous membranes or other soft tissues in the genital areas. No one knows if the virus can penetrate the lining of the male urethra, the tubelike passage through which urine flows.

Q. What is the risk of getting the virus from a single act of vaginal intercourse with an infected person?

Precise data are lacking. From indirect evidence, Federal scientists judge the risk of transmission in a single encounter to be low. Quantification is complex: Some infected people have said they had only a single exposure, while other people who have had hundreds of exposures have escaped infection. Still, several studies have shown that with repeated intercourse, as many as half the sexual partners of infected men or women become infected.